In one conventional form of quarter-turn, on-off valve, the valve includes a cylindrical plug rotatable in a through hole in a valve body. A handle is provided on an exposed portion of the plug for rotating the plug 90.degree. to either align or disalign a through hole in the plug with the inlet and outlet ports at opposite ends of the body.
It is conventional in such plug valves to provide a through bore extending axially perpendicular to the flow path between the inlet and outlet ports. The plug protrudes through both the top and bottom of the body in the bore and is sealed therein by elastomeric O-rings provided in annular grooves at opposite ends of the plug.
It is further conventional to provide an O-ring on the surface of the plug 90.degree. from the plug's flow path bore, which seats about the inlet port, so as to seal off the port when the plug is rotated to the off position.
The axial positioning of the plug within the body is controlled by means of a snap ring located in an annular groove at the bottom end of the plug and by the handle, which is larger than the plug-receiving bore in the body at the other end of the plug.
A locating pin is conventionally pressed into a hole at the top of the body parallel to the axis of the plug and engages stops integral with the plug to provide rotational limit stops for the plug.
The conventional plug valve, as discussed above, is disadvantageous in the requirement of the provision of seals at both ends of the plug. Further, the projection of the plug at the bottom of the valve is disadvantageous in that such exposure thereof may result in interference with the free rotation of the plug, as by an adjacent object contacting the lower end of the plug. Further, the conventional stop pin provided for limiting the rotation of the plug is openly exposed to dirt and foreign matter which may, under adverse conditions, undesirably restrict full rotation of the plug between the on and off positions.